The invention relates to an apparatus for simultaneously writing a plurality of data signals in parallel data tracks in a longitudinal direction on a recording medium, the apparatus comprising
a head having a plurality of write units which are positioned adjacent to each other in a transversal direction which is transverse to said longitudinal direction, which write units directly adjoin each other in the transversal direction and
transport means for moving the head and the recording medium relative to each other in the longitudinal direction.
The invention also relates to an information storage system comprising a recording medium and an apparatus for simultaneously writing a plurality of data signals in parallel data tracks in a longitudinal direction on the recording medium, the apparatus comprising
a head having a plurality of write units which are positioned adjacent to each other in a transversal direction which is transverse to said longitudinal direction, which write units directly adjoin each other in the transversal direction and
transport means for moving the head and the recording medium relative to each other in the longitudinal direction.
The invention further relates to a method of simultaneously writing a plurality of data signals in parallel data tracks in a longitudinal direction on a recording medium with a head having a plurality of individually addressable write units which are positioned adjacent to each other in a transversal direction which is transverse to said longitudinal direction, which write units directly adjoin each other in the transversal direction, the head and medium being moved relative to each other in the longitudinal direction.
Such an apparatus, such a system and such a method are known from WO-A-97/33274. The known apparatus is suitable for co-operation with a magnetic tape. The apparatus has two reel spindles to move the magnetic tape past a thin-film magnetic head in a longitudinal direction. The magnetic head comprises a head face with a plurality of write units which adjoin each other in a transverse direction which is transverse to the longitudinal direction. A plurality of parallel data tracks can be simultaneously written on the magnetic tape with these write units. Because the write units directly adjoin each other, a large number of tracks can be written on the tape.
It is an object of the invention to provide an apparatus as defined in the preamble, which is compatible with apparatuses of an older generation. To achieve this object, the apparatus according to the invention is characterised in that the apparatus comprises switching means to switch the apparatus
from a normal mode wherein each data signal is coupled to a single write unit to write data tracks with a first track density, each data track being written by a single write unit,
to a combination mode wherein each data signal is coupled to a group of parallel, adjoining write units to write data tracks with a second track density which is a portion of the first track density, each data track being written by such a group of write units. The second track density may be a fraction of the first track density. Due to these measures, data tracks with two different track densities can be written with the same magnetic head. This is very advantageous because the replacement of a first generation apparatus by a second generation apparatus according to the invention with a greater data track density does not require the xe2x80x9coldxe2x80x9d tapes recorded by the first generation apparatus to be transferred to a second generation tape in order to be able to update the information stored on them with the second generation apparatus. Instead the xe2x80x9coldxe2x80x9d tapes can be updated by the second generation apparatus because it can also write with the track density of the first generation apparatus. By writing the old tapes with the track density of the first generation apparatus the recording is more reliable and the data can be read by apparatuses of the first generation. It is very important that the write units directly adjoin each other in the transversal direction because the apparatus must be able to overwrite data already recorded on the medium. If there would be a gap between two write units of a group, xe2x80x9cold dataxe2x80x9d written by a first generation apparatus would remain on the recording medium. This old data would disturb the read-out of the newly recorded data by a first generation apparatus. With the measures according to the invention, it is achieved that the apparatus is compatible with apparatuses of an older generation.
It is to be noted that EP-A-0 427 008 shows a helical scan unit having two adjacent magnetic heads which can be switched in parallel to obtain a synthetic unit formed by the units of the two adjacent magnetic heads. However, this apparatus is not suitable for simultaneously writing a plurality of parallel data tracks.
The measure as defined in dependent claim 2 has the advantage that it enables a great track density to be achieved. Because the units are spaced in the longitudinal direction there is more space to construct the write unit and there is more space to make electrical connections. For example, a magnetic head as disclosed in WO-A-97/33274 (incorporated herein by reference) can be used. Preferably, a thin-film magnetic head is used. By adding the specified delay in the combination mode, the phases of the track parts written by the first write unit and the second write unit are matched. As a result these tracks can be read with a first generation apparatus having read units with a width corresponding to the track width.
The measure as defined in dependent claim 3 has the advantage that a very great track density can be achieved. Because the magnetic head can actively follow the servo track during writing and/or reading, the data track width can be made smaller than the movements of the medium in the transversal direction during recording and thus the data track density can be increased considerably. For example, the servo could be a buried servo system as described in WO-A-96/30897 (incorporated herein by reference).
The measure as defined in dependent claim 4 has the advantage that the track density is optimal both in the combination mode and in the normal mode.
The measures as defined in dependent claim 5 have the advantage that information can be recorded with three different track densities. This is advantageous when three generations of a recording system are used for reading and/or writing the same set of recording media.
The measure as defined in dependent claim 6 has the advantage that the apparatus automatically selects the right mode dependent on the data track density on the recording medium. This detection can be performed for example by comparing signals from adjacent read units or by detecting a property, for example the presence of a hole, of a cassette in which the recording medium is housed.
The system according to the invention is characterised in that the recording medium comprises at least one servo signal present in a servo track extending in the longitudinal direction, and in that the apparatus comprises
an actuator for positioning the head and the recording medium relative to each other in the transversal direction,
at least one read unit to read the at least one servo signal from the recording medium and
servo means adapted to drive the actuator dependent on the servo signal read by the read unit so that the head will follow the servo track, and in that the apparatus comprises switching means to switch the apparatus
from a normal mode wherein each data signal is coupled to a single write unit to write data tracks with a first track density, each data track being written with a single write unit,
to a combination mode wherein each data signal is coupled to a group of parallel, adjoining write units to write data tracks with a second track density which is a part of the first track density, each data track being written by such a group of write units.
The measure as defined in dependent claim 8 has the advantage that a servo signal can easily be generated by comparing the signal from one read unit with that from the other unit. The sensitivity of this servo signal is increased when the dimension of the read units in the transversal direction is reduced. This is advantageous as later generations will employ a greater track density, resulting in smaller read units, but also require a better positioning accuracy of the head relative to the recording medium because the tracks are narrower. Hence, the recording medium can be used by different generations of apparatuses employing a tracking servo.
The method according to the invention is characterised in that each data signal is coupled to a group of adjoining write units so that each data track is written by such a group of write units.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereafter.